This invention relates to a thin-film magnetic head, a magnetoresistance effect magnetic head and a composite magnetic head which are suitably adapted for recording and reproducing information signals into and from, for example, a hard disk.
A magnetoresistance effect magnetic head, hereinafter referred to as an MR head, has its magnetic sensor formed of a magnetic thin film having magnetoresistance effect. Since resistivity of the magnetic thin film is changed in accordance with a signal magnetic field based on magnetic recording into a magnetic recording medium, the magnetic sensor detects the change in resistivity as a reproduction output voltage from a sense current flowing through the magnetic thin film.
Such an MR head has characteristics, such as, high output, low crosstalk and velocity-independence, and is therefore used as a reproducing head for a hard disk drive (HDD) or as a high density recording/reproducing head for a digital audio tape recorder.
This MR head is exemplified by an MR head of shield structure as shown in FIG. 1.
The shield MR head 100 of FIG. 1 has an MR element 101, which is formed of a single-layer or multi-layer magnetic thin film having magnetoresistance effect and is arranged in a space forming a predetermined reproduction gap G.sub.R between an upper (layer) shield core 102 and a lower (layer) shield core 103. The MR element 101 is electrically connected with a pair of electrodes 105a, 105b for causing a direct current as the sense current to flow and for outputting the change in resistivity as a change in voltage.
Between the electrodes 105a, 105b, a bias conductor 104 for applying a bias magnetic field to the MR element 101 is provided, traversing the MR element 101. For the shield cores 102, 103 of the shield MR head 100, a single bulk magnetic body, a single-layer plating film or a single-layer sputtered film is used.
An example of a composite magnetic head, produced by combining an MR head with a recording head formed of an inductive thin-film magnetic head, is shown in FIG. 2. The inductive thin-film magnetic head and the composite magnetic head are hereinafter referred to as an inductive head and an MR inductive head, respectively. Since the MR head in this case has the structure similar to that of the example in FIG. 1, the corresponding parts are denoted by the same reference numerals and will not be explained further.
In FIG. 2, a magnetic core 106 is provided on the upper shield core 102 of the MR head with a predetermined recording gap G.sub.W between them, and a spiral head winding 107 is provided, surrounding a magnetically connecting part as a connecting portion of the magnetic core 106 with the shield core 102.
In the MR inductive head of this structure, the lower shield core 103 is provided on a base or substrate 108 of Al.sub.2 O.sub.3 --TiC, and a protection film layer 109 is stacked on the magnetic core 106, with a non-magnetic insulation material charged or stacked between the gaps. The end surface of the MR inductive head having the reproduction gap G.sub.R and the recording gap G.sub.W formed therein serves as an air bearing surface (ABS), that is, a surface facing the magnetic recording medium, such as a hard disk.
Meanwhile, the magnetic core 106 and the shield cores 102, 103 are normally provided with anisotropy in a particular direction, that is, the direction of track width, in the production process. However, it is difficult to provide anisotropy on the entire film of the magnetic core 106 and the shield cores 102, 103, and dispersion of anisotropy usually remains in a microscopic sense. Such dispersion of anisotropy is a cause of a noise generated by fluctuation in output and shifting of magnetic domain walls, that is, a so-called Barkhausen noise. Also, the magnetic ununiformity causes fluctuation at the time when the magnetic field is externally added, resulting in fluctuation of reproduction output after recording.
If a two-gap recording/reproducing head is employed in which the inductive head is superposed on the MR head, or if a one-gap recording/reproducing head is employed in which the magnetic core of the inductive head serves also as the shield core of the MR head, a large magnetic field is applied from a recording head section to the shield core on recording. For this reason, a magnetic domain of the shield core may remain turbulent when the operation has been switched from recording to reproduction. Since the shield core forms part of a magnetic path of the magnetic field from the magnetic medium, there is a high possibility that the turbulence of the magnetic domain of the shield core causes the Barkhausen noise to be generated. In addition, since the shield core forms part of a magnetic path of the magnetic bias, the state of bias becomes unstable, causing the reproduction signal waveform to be unstable.
The JP Patent Kokai Publication No. 5-62131, for example, discloses a technique of maintaining a reproduction output at a constant level by splitting the thin-film magnetic core into two films with the non-magnetic layer between them and then reducing the leakage magnetic field from the thin-film magnetic core to the MR element. Also, attempts to restrict changes in the magnetic domain due to the recording magnetic field have been made with the use of a shield core formed of a magnetic film of two layers or more which is separated with the non-magnetic film and stacked. However, it is difficult to perfectly stabilize the magnetic domain and to have a perfectly single magnetic domain for stabilizing reproduction signals.
Meanwhile, it has been known that the Barkhausen noise can be reduced by applying the magnetic field in the direction of the easy axis. Thus, a technique of causing a current to flow through the two-layer shield core to stabilize the reproduction output has been conceived. However, even with this technique, it may be impossible to perfectly adjust the magnetic domain which has become turbulent on recording, particularly in the MR inductive head.